Conventional oil level dipsticks having a fluid level indicating rod for insertion into a chamber containing oil such as a crankcase or oil reservoir of a reciprocating apparatus generally require that the apparatus be stopped at the time of the oil reading. This is due to agitation of the oil by the reciprocating apparatus, and variations in the pressure of the air above the oil caused by the reciprocating apparatus. Pressure variations of the air cause air containing oil to be expelled on the positive pressure portions of the cycle of the reciprocating apparatus, and negative variations of the air pressure cause unfiltered air to be drawn into the oil chamber.
U.S. Pat. No. 3,662,470, which issued on May 16, 1972, provides an approach to solving this problem. The teachings this patent are hereby incorporated into the present application by reference thereto.
In the cited patent, a tube is provided for insertion of an oil level indicating rod into the chamber which contains the oil. A ball valve at the lower end of the tube is provided to prevent flow of air and oil between the chamber and the atmosphere. When the oil level indicating rod is inserted, it pushes the ball downward thus opening the ball valve, so that the oil level in the tube equalizes with the oil level in the chamber. A seal is provided between the top end of the tube and a portion of the oil level indicating rod to prevent flow of air and oil when the ball valve is opened by insertion of the oil level indicating rod.
The seal at the top end of the tube consists of compressible sealing means which are compressed when the level indicating rod is fully inserted. To provide a partial seal during brief times when the indicating rod is being inserted or removed, a portion of the rod has a portion on its O.D. threaded like a bolt, and a portion of the tube has a portion on its I.D. threaded like a nut. These fit closely and prevent significant flow of oil and/or air past the rod.
This patent also cites a port in the tube at a high elevation in the chamber. The patent indicates that this serves to prevent undesirable rise of oil above the level of the port. This port also serves to equalize pressure of the air above the oil in the tube and the pressure of the air above the oil in the chamber, so that the oil level in the tube represents the level of oil in the chamber.
This patent, while a major advance over the art which preceded it, has several disadvantages:
(1) It is expensive, requiring the assembly of eleven parts. PA1 (2) The ball valve of this patent requires a moveable sleeve mounted externally to cover a lower portion of the tube. This arrangement has considerable slop or play, and is prone to damage because of its exposed external location. PA1 (3) If servicing is necessary, it is difficult to disassemble and repair.